(1) Field of the Invention
The present invention is related to a mounting structure for mounting, onto an edge of the rotating shaft, a power transmission body such as a gear or a pulley for transmitting power to the rotating shaft, and to a toner transportation device that includes such a mounting structure.
(2) Description of the Related Art
In some image forming apparatuses that form an image by electrophotography, a toner image formed on the surface of a photoconductor drum is transferred, for example, to an intermediate transfer belt or a recording sheet, after which a cleaning device collects toner remaining on the surface of the photoconductor drum.
Such a cleaning device is provided with a cleaning blade, a housing, and a toner transport screw. The cleaning blade scrapes remaining toner off of the surface of the photoconductor drum and is provided in the housing. The housing stores the toner scraped off by the blade. The toner transport screw transports the toner in the housing in a predetermined direction. The toner that is transported by the toner transport screw is ejected outside of the housing and collected.
The toner transport screw is composed of a rotating shaft along which a spiral transport blade is provided. The transport blade rotates integrally along with the rotating shaft. As a result, toner is transported in a predetermined direction by the transport blade.
One edge of the rotating shaft in the toner transport screw passes through a through-hole provided in a side panel of the housing so as to protrude outside of the housing. A gear with an axial hole is mounted on the protruding edge of the rotating shaft. Having been mounted onto one edge of the rotating shaft, the gear is rotatably supported within the through-hole provided in the side panel of the housing so as to be able to rotate integrally with the rotating shaft. Rotary force from a motor or the like is transmitted to the gear, and rotation of the gear causes the rotating shaft to rotate.
On the inside of the housing, a seal member is provided on the rotating shaft to seal the through-hole. The seal member is formed from an elastic material, such as a sponge, and is fit to the rotating shaft. The seal member is pressed against the side panel around the through-hole by a flange provided on the rotating shaft.
Outside of the housing, the reaction force of the seal member provided in this way causes the gear that is retained against the rotating shaft to be pressed against by the side panel of the housing. This may cause a large force to act on the retaining portion of the rotating shaft that pushes the gear against the side panel of the housing. It thus becomes necessary to adopt a structure such that even if a large force acts on the retaining portion of the rotating shaft, the retaining portion will not easily stop retaining the gear.
In order to retain the gear mounted on the rotating shaft, usage of an E-ring retaining ring is well known. Since an E-ring is mounted in a groove formed at the edge of the rotating shaft, however, it is necessary to form the groove along the entire circumference of the rotating shaft at the edge thereof. The toner transport screw is normally formed by integrally forming the rotating shaft and the transport blade from synthetic resin, the rotating shaft having a small diameter of 3 mm to 5 mm. Forming a groove along the entire circumference of the rotating shaft with this small diameter drastically reduces the strength of the rotating shaft.
As a result, if a large force in the axial direction, directed away from the side panel, is applied to the E-ring from the gear attached to the rotating shaft, the rotating shaft may easily break, making it impossible to retain the gear against the rotating shaft.
Apart from an E-ring, another known method for retaining the gear is to use a snap-fit with a contractible outer diameter at the tip thereof.
Patent Literature 1 (Japanese Patent Application Publication No. 2002-135522) discloses a snap-fit, formed from synthetic resin, that rotatably supports a swinging gear while retaining the swinging gear. The snap-fit disclosed Patent Literature 1 has a conical tip. The tip has a larger outer diameter than the outer diameter of the shaft supporting the swinging gear. A hole is formed along the central axis of the conical tip, and the outer diameter of the tip contracts upon application of external pressure due to contraction of the hole.
When the outer diameter of the tip of the snap-fit contracts due to external pressure, the snap-fit can pass through a gear hole provided along the central axis of the swinging gear. Upon release of the external pressure, the outer diameter of the tip becomes larger than the gear hole, so that the tip engages with the portion of the swinging gear around the gear hole. As a result, the gear is prevented from coming free from the snap-fit.
In order to reliably prevent the swinging gear from coming free from the snap-fit disclosed in Patent Literature 1, the outer diameter of the tip of the snap-fit may be increased so that the area of the tip that is engaged with the swinging gear increases. In this case, however, in order for the tip of the snap-fit to pass through the gear hole in the swinging gear, it is necessary to increase the size of the diameter of the hole provided along the central axis in order for the outer diameter of the tip of the snap-fit to contract greatly.
Increasing the diameter of the hole along the central axis, however, reduces the strength of the entire tip, thus placing a limit on the extent to which the outer diameter of the tip can be caused to contract. The snap-fit disclosed in Patent Literature 1 thus does not allow for an increase in the area of the region where the tip of the snap-fit and the gear engage. Therefore, this snap-fit leads to the risk of not being able to reliably retain a gear on which a large force acts in the axial direction of the rotating shaft, as in the rotating shaft of the toner transport screw in the above-described cleaning device.